High frequency current measuring device



Amai 15, v1941., H. WEHRUN 2,238,298

HIGH FREQUENCY CURRENT MEASURING DEVICE Original Filed Feb. 18, 1937wam/6 CoA/raaf ratnta Apr. 1s, 194i Hans Wehl-lin, Gumligen; near Berne,Switzerland, assigner to C. Lorenz Aktiengesellschaft; Berlin-Tempelhof,Germany, a company original application February 1s, 1937, serial No.l

ber'22, 1938, Serial No.

February 18, 1936 Divided andthls application Septem- -23l,181. InGermany 8 Claims. (C l. lil-95) My invention relatesto high frequencycurrent measuring devicesfemployed in combination withlcurrenttransformers for indicating at a remote Point the value of a highfrequencycurrent iiowlng -in aconductorline. Suitablecurrenttransformersfor` cooperating with the device hereinafter described areset forth inmy copending United States patent application Serial No. 126,531,'nowPatent No. 2,214,915, entitled High frequency current transformers, ledon February 18, 1937, 10

ofwhich applicationrthis is a division.'-

It is a well -known expedient to employ current v.transformers when highfrequency currents are -to be measuredat a remote point by means of highfrequency current-metering devices. If such devices would be interposedin the high frequency conducting linel the space capacity of themetering device would -amount to an unpermissible value, while the spacecapacities-may be considerably reduced-in connection with current trans-My invention consists in certain features ofnovelty which will be fullyunderstood from the following description and be pointed out in. the

appended' claims, reference being hadto the 'ac- 25 companyingdrawinginwhich Fig. 1 shows one embodiment according to the-invention, while Fig.2 illustrates-a modification of lthe arrangement shown in Fig.- 1.

In Fig. 1 the left por-tion shows a current transformer, while the rightportion thereof represents the current'metering device. The currenttransformer consists of a conductor I which constitutes .theprimarywinding of the transformer.

vThe secondary winding thereof is denoted 1I. 35

This secondary coil is'fmounted relative to the conductor IJ-by means ofa supporting member i K of insulation. The line T interconnecting thecurrenttransformer andthe measuring device is electrically associatedwith the secondary coil Yi0 II ofthe current transformer.

The measuringdevice comprises a direct current indicator Mrand a-thermo-electric-couple E' -interconnted with one another. If the.thermocouple E and' the' indicator M are n qt combined 45 ages in theIcase of wire breakage on the'secondin one unit, the line L'interconnecting -these two devices should be carefully screened by atube T', since this line would otherwise pick up disturbing highfrequency current from Vconductor I. Since `the thermo-electric-couple Ebecomes heated by I a high `frequency current picked up by the line L',the indicator M would deiiect its pointer and thus give a wrongindication. If the most careful shielding is not suiilcient toobviatethis drawbe interposed between the thermo-couple E and the indicator Min order to prevent high frequency energy picked up by the-line L' vfromaecting the thermo-couple. -An arrangement of the last mentioned typemight be positioned between the current transformer and the thermocouple E in cases Where the measuring .devie is protectedv againstcurrents which arel picked up by the line L'. 'I'he thermorcouple andchoking device assembly may be arranged in a shield F common thereto.

If the line interconnecting the current transformer andthe'thermo-electric-couple E or indicator M is longer than oneequarterof the operating wavelength, the screening'tube T is preferablypartially given a helical shape as shown at t so that the conductor jinthe interior of the shielding T presents the shape ofa choke coil,'which may be provided' with a core Fe' of high frequency iron. Theshielding T is grounded by means of'conductor u between the secondarycoil II of the current `transformer and the helical portion tof 'theline, preferably at a current -anti-node or a potential node. If adenite operating frequency is'employed, a condenser C may be connectedacross the helical portion 't in order to'provide anarrester or rejectorcircuit which is tuned tov the operating frequency.

The modification shown in Fig. Z'involves the feature that the measuringdevice assembly EM is detachably and exchangeably associated with -theline. 'I'his is accomplished by the agency of plug contacts e, 'e'adaptedto.be inserted in sleeves o, o" to which the secondary coil ofthe current transformer is connected over the line L. Care should betakenthat the transformer is automatically shortrcircuited whenremovingthe device E, M from the plug sleeves o, o', since otherwise veryconsiderably high frequency voltages may persist at these sleeves. Oneexample of an arrangement provided for this purpose is shown in theshape of a contact spring N which tends to make vcontact with the sleeveo' when the plug e is withdrawn from its corresponding sleeve o.Moreover, .the occurrence 'of high voltary side can be obviatedby a glowdischarge tube f H shunted across the two lines L.

What is claimed is: 1. A high frequency meter assembly comprisin a highfrequency current transformer, a high frequency current measuring devicecomprising a thermo-electric-couple, a. shielded conductor lineinterconnecting said transformer and said back, a chokeor a filter chainmay suitably thermo-electric-c'ouple, a direct, current indica- ,i ofsaid assembly.

'said coil.` V' 5, Ahigh frequency I f 1 tor, shielded meansinterconnecting said thermoelectric-couple and said direct currentindicator,

casacca x a high frequency current transformer', ahighfrequency-.current measuring device-comprising a.

anda choke means formed 'from said shielded' conductor line interposedbetween said trans- '.former and said high f requency'measuring deviceat a point near said measuring device.

2. A high frequency meter assembly comprising a high frequency currenttransformer, ahigh frequency current measuringdevice comprising a' saidhigh frequency measuring device at a point near said measuring device,and` means for tuning said choke means to theoperati'ng frequency ,3. Ahigh frequency meter assembly comprising a high frequency currenttransformer, a high fre- A quency' currentmeasuring devicecomprising a-thermo-electric-couple, a shielded conductor'line 'interconnecting saidtransformer and said ther- -Vmo-electric-couple, a direct currentindicator, a-

thermo-electric-couple, a shielded conductor line `longer 4than-a;4quarter. wavelength at the voperat-4 ifing frequency interconnecting'vsaid transformer and said thermo-electric-cople. a direct currentindicator, shielded means interconnectingsaid thermo-electric-couple andsaid direct currentindicator, a helical coill formed in said conductorfrom the part spaced more than a quarter wavelength fromsaid'transformer, a tuningcondenser connected across the helical turns ofsaid coil,

and 4means grounding said conductor shield at a I 'point spacedsubstantially a: quarter wavelength from said transformer.

6. vA highfrequency meter assembly comprising a high frequency currentItransformer, a high frequency current Imeasuring device comprising asecond shielded conduc'etor-,line interconnectingsaidthermo-electric-coupie and said direct-current indicaton'nn'dhighfreqe'ncy choke means 4interposed in each of saidfconductor lines toisolltc said high 'frequencycurrent device from high frequencyinterference.

4. A high frequency meter assembly comprising a high frequency currenttransformer, a high frequency current measuring device comprising Vathermoelectriccouple. a shielded conductor line v longer thanl a quarterwavelength at the operating frequency interconnecting saidtransformerand said thermo-electric-couple.a direct current indicator,shielded means interconnecting said thermo-electric-couple and saiddirect-current indicator, and a helical coil formed in said conductorfrom the part spaced more than a quarter wavelength from saidtransformer. .and a tuning condenser connected across the helicalturnsof meter assembly comprising thermofelectric-couple, a shieldedconductor line longer than a quarter wavelength at the operating;frequency interconnecting said transformerand saidthermo-electric-couple, -a direct current indicator, shielded meansinterconnecting said vthermoelectric-couple and said direct currentindicator, a helical coil 'formed in s aid conductor from the par-tspaced more than a quarter wavelength from said transformer, a' highfrequency icon core in, said4 helical coil, and a tuning condenserconnected across thehelical turns 'of said coil."

II A high frequency assembly according 'to claim 1,. wherein thethermo-electric-couple and direct current-indicator are comprised in onedevice', further comprising plug contacts fitted to said high frequencymeasuring device, and plug sleeves connectedvto vthe' secondary coil oi'said .transformer to receive said plug contacts.

8.';A high frequency :ssisexnblyv according to claim 1, 'wherein thethermo-electric-couple -and vdirect current indicator are comprised inone de vice, further comprising plug contacts fitted to said highfrequency measuring'v device, plug -1-sleeves connected to lthesecondary coil of said transformer to receive said plug contacts, and

means' tov short circuit said secondary coil upon removal-of saidinstrument.

